According to the prior art automatic transmissions, particularly those for motor vehicles, comprise planetary gearsets shifted by means of frictional or shift elements such as clutches and brakes, and are usually connected to a starting element that can operate with slip and is optionally provided with a bridging clutch, such as a hydrodynamic torque converter or a fluid clutch.
Such automatic transmissions are known for from DE 199 49 507 A1 by the present applicant, which describes a multi-stage transmission in which two non-shiftable upstream gearsets are provided on the transmission input shaft, which on their output side produce two speeds which, besides the speed of the drive input shaft, can be selectively engaged with a shiftable, double planetary gearset that acts upon the drive output shaft by selective engagement of the shift elements used, in such manner that to shift from one gear to the respective next-higher or next-lower gear, of the two shift elements actuated at the time in each case only one shift element has to be engaged or disengaged. Using five shift elements this enables seven forward gears to be produced, whereas if six shift elements are used, nine or ten forward gears can be obtained.
Furthermore, from DE 102 13 820 A1 a multi-stage automatic transmission with eight forward gears and one reverse gear is known, which comprises a first input path T1 of a first transmission gear ratio; an input path T2 which has a higher gear ratio than the input path T1; a planetary gearset of the Ravigneaux type with four elements, the four elements being a first element, a second element, a third element and a fourth element in the sequence of the elements in a speed diagram; a clutch C-2 which transmits rotation of the input path T2 to the first element S3; a clutch C-1 which transmits the rotation of the input path T2 to the fourth element S2; a clutch C-4 which transmits the rotation of the input path T1 to the first element; a clutch C-3 which transmits the rotation of the input path T1 to the second element C3; a brake B-1 which brings about the engagement of the fourth element; a brake B-2 which brings about the engagement of the second element; and a drive output element which is coupled to the third element S3.
Moreover, a 9-gear multi-stage transmission is known from DE 29 36 969 A1; it comprises eight shift elements and four gearsets, such that one gearset serves as an upstream transmission and the main transmission comprises a Simpson gearset and a further gearset that serves as a reversing gear.
Other multi-stage transmissions are known, for example from DE 102005010210 A1 and DE 102006006637 A1 by the present applicant.
In general automatically shifted vehicle transmissions of planetary design have often been described in the prior art and undergo constant further development and improvement. Such transmissions should take up little structural space, in particular having a small number of shift elements, and in sequential shift operations should avoid double shifts, so that when shifting in defined gear groups in each case only one shift element is changed.
From the as yet unpublished DE 102008000428.3 by the present applicant, a multi-stage transmission of planetary design is known, which comprises a drive input and a drive output arranged in a housing. In this known transmission are provided at least four planetary gearsets, called the first, second, third and fourth planetary gearsets in what follows, at least eight rotating shafts, called the drive input shaft, the drive output shaft and the third, fourth, fifth, sixth, seventh and eighth shafts, and at least six shift elements, including both brakes and clutches, whose selective engagement produces various transmission gear ratios between the drive input and the drive output, such that preferably nine forward gears and one reverse gear can be obtained.
In this case the first and second planetary gearsets, which are preferably designed as minus planetary gearsets, form a shiftable upstream gearset whereas the third and fourth planetary gearsets form a main gearset.
In this known multi-stage transmission it is provided that the carriers of the first and second planetary gearsets are coupled to one another by the fourth shaft, which is connected with an element of the main gearset, the ring gear of the first planetary gearset is coupled to the sun gear of the second planetary gearset by the eighth shaft, which can be releasably connected by means of a first clutch to the drive input shaft, and the sun gear of the first planetary gearset can be coupled, via the third shaft, by means of a first brake to a housing of the transmission and can be releasably connected by a second clutch to the drive input shaft, whereas the ring gear of the second planetary gearset can be coupled via the fifth shaft by means of a second brake to the housing of the transmission. Furthermore, the seventh shaft is permanently connected to at least one element of the main gearset and can be coupled by a third brake to the transmission housing, whereas the sixth shaft is permanently connected to at least one further element of the main gearset and can be connected releasably to the drive input shaft by a third clutch; the drive output shaft is connected permanently to at least one other element of the main gearset.
Preferably, in the known transmission the fourth shaft is permanently connected to the ring gear of the third planetary gearset, the sixth shaft is permanently connected to the ring gear of the fourth planetary gearset and to the carrier of the third planetary gearset, and can be connected releasably by means of the third clutch to the drive input shaft. In addition, the seventh shaft is connected permanently to the sun gears of the third and fourth planetary gearsets and can be coupled by means of the third brake to a housing of the transmission. In this case the drive output takes place via the drive output shaft connected permanently to the carrier of the fourth planetary gearset. Moreover, the third and fourth planetary gearsets can be combined or reduced to a Ravigneaux gearset with a common carrier and a common ring gear.